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golfpro
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So is it even less desirable to have NO contamination than NO2? what temp should my oil bath be?
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Pulverulescent
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NO is a product of nitrogen oxidation and is further oxidised to the red NO2 form by contact with oxygen.
Oil-bath temps shouldn't go much above 121°C as this is the azeotrope's max boiling temp..
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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golfpro
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Somehow I had in my mind that nitric acid distilled from a sulfuric mix get's an acid that is higher than the 70% azeotrope because the sulfuric can
dehydrate the nitric a bit.
I really wish I had some of that liquid acid-base indicator, use a few drops and it turns purple once it hits a basic solution, I could easily titrate
the nitric acid and know the exact concentration. Distilling from a retort with nitrate salt and sulfuric, some people here have said gives 50%, and
others said gives closer to 85%-92%.
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bfesser
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<a href="http://en.wikipedia.org/wiki/Phenolphthalein" target="_blank">Phenolphthalein</a> <img src="../scipics/_wiki.png" />
solution?
[Edited on 7/20/13 by bfesser]
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golfpro
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Ya.
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Oscilllator
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Pulverulescent I'm afraid your idea doesn't hold up. If the red NO2 was being swept away by increased HNO3 vapors, then surely once the HNO3 had been
condensed then the red NO2 would re-appear. This is not what happened, almost no NO2 was observed coming from the vacuum take-off adaptor at the time
when the flask was clear. But when the flask was filled with NO2 then NO2 vapor were observed coming out from the vacuum take-off.
weiming's explanation seems more likely to be correct, since I don't have a still head that a thermometer can be attached to, so I cant monitor the
temp of the distillation. Since I was using a sand bath, it is entirely possible the temperature reached over 150C
And yes golfpro, HNO3 obtained by distillation can easily be over the azeotropic concentration, although I don't have any exact figures.
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hissingnoise
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| Quote: | | I'm afraid your idea doesn't hold up. If the red NO2 was being swept away by increased HNO3 vapors, then surely once the HNO3 had been condensed then
the red NO2 would re-appear. |
Look, it's really quite simple; nitric acid decomposes on heating ─ NO2 will not dissociate because the vapour temp. in the flask
won't normally reach 150°C!
Even if it did, it would reform on cooling . . .
But then again, you just may have spotted an anomaly that has eluded other scientists for these last few centuries?
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Pulverulescent
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Ooops! 'Used my alter ego by mistake . . .
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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Oscilllator
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Quote: Originally posted by hissingnoise  | | Quote: | | I'm afraid your idea doesn't hold up. If the red NO2 was being swept away by increased HNO3 vapors, then surely once the HNO3 had been condensed then
the red NO2 would re-appear. |
Look, it's really quite simple; nitric acid decomposes on heating ─ NO2 will not dissociate because the vapour temp. in the flask
won't normally reach 150°C!
Even if it did, it would reform on cooling . . .
But then again, you just may have spotted an anomaly that has eluded other scientists for these last few centuries?
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If the nitric acid is decomposing and the NO2 isn't dissociating, then why isn't there a visible red colour? You appear to be just contradicting me,
and not offering an alternate view.
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Pulverulescent
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OK! Nitrogen dioxide exists in equilibrium with its colourless dimer; N2O4 ↔ NO2!
Heat shifts the equilibrium to the right, deepening the colour.
During distillation, hot, red NO2 fills the flask initially, but as ebullition increases this is largely displaced by HNO3
vapour.
The cooled vapour condenses, dissolving NO2 and lemon-coloured acid drips from the condenser!
A small quantity of NO2 escapes the condenser, depending on cooling-water temp. but the distillate contains most of the NO2
produced!
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones"
A Einstein
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Oscilllator
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OK! Phenomena explained! Nice use of excessive exclamation marks!
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ElizabethGreene
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Hi!
Titration is the way to answer this question. If you don't have a pH indicator, get some red cabbage and make some. To make it, shred the cabbage
and boil about a cup of it in two cups of water. After 10 minutes, drain it filter it with a food safe filter retaining both components. The solid
component is delicious with salt and pepper. The liquid component is an effective pH indicator. Addition of 10% by volume of drugstore isopropyl
alcohol will prevent it from going rancid.
Calibrate it using solutions of Vinegar (CH3COOH), HCl, NaOH, and NaHCO3.
Conveniently, the solutions of NaOH and HCl are what you need to titrate acids and bases respectively.
Cheers,
Greene
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golfpro
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Nitric Acid from Retort.
Hi,
I distilled approx. 10ml nitric acid from 50ml sulfuric acid/38gram KNO3, I used an oil bath and heated up to about 140* C, it took about 15 minutes.
Well I had a gram peice of silver I added to 10ml Nitric Acid and no reaction at all, then I add my 10ml to hot oil bath, some nitrogen dioxide gas
was made, but still the silver peice looks exactly the same, is my nitric not strong enough?.
My nitric acid is kind of yellowish from nitrogen dioxide contamination, but I did use a retort..
Thanks
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bfesser
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You may need to dilute it slightly with water. Dissolution will be slow. Apply gentle heating. Be patient.
[Edited on 7/25/13 by bfesser]
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annaandherdad
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You will have to heat the HNO3 if you want an appreciable rate of reaction with a lump of silver. I found 70-80C was about right, using 20-30% HNO3.
I would guess that more dilute acid will work fine, too, as long as it is heated. The reaction with silver is pretty slow at room temperature.
On the other hand, NHO3 reacts rapidly enough with silver powder or dust at ordinary temperatures, in my experience, in which I have used silver
powder created by reduction of silver chloride in an alkaline solution of glucose.
There's a Nurdrage video on this.
Any other SF Bay chemists?
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woelen
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I think that the acid is too concentrated. Some metals are passivated by highly concentrated acid. Try mixing the acid with half its volume of water
and then add the silver.
You could also try adding other metals. Copper reacts violently with nitric acid, giving dense brown fumes. If the acid does not react with copper,
then add half its volume of water and swirl. If it still does not react with copper, then it is no nitric acid or something which only contains a
small amount of nitric acid.
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golfpro
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I got it, I had to use a good amount of heat though, actually some silver nitrate precipitated as crystals after the acid cooled.
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kilowatt
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I don't believe that the acid from a simple retort is much less concentrated than if you had used a full reflux column, especially if you did an
anhydrous reaction. Even with a wet reaction, should be getting pretty close to azeotropic once the water is off.
I once dissolved a roughly 1oz lump of sterling silver in concentrated nitric acid at room temperature, before knowing that the dilute acid was more
effective in that case. While the copper went into solution, silver nitrate slowly formed as white crystals over the course of about a year before the
silver was gone. Definitely not a rapid process. I suppose the more readily dissolving copper it more difficult in that case, if pure silver dissolves
relatively more readily.
[Edited on 26-7-2013 by kilowatt]
The mind cannot decide the truth; it can only find the truth.
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golfpro
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Storing concentrated Nitric Acid
Hi,
I have these dark brown glass bottles with black plastic lids, these are not acid bottled though and I was thinking I could store some nitric in
this? I didn't know if the HNO3 vapours would attack the lid though, or if I might be better off trying to seal the top with aluminum?
Thanks
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bfesser
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Does the inside of the cap have a transparent plastic cone? Your best off just finding a bottle with a PTFE-lined cap.
Also, storing nitric acid has been discussed to death. Please use the <img src="./images/xpblue/top_search.gif" /> <a
href="search.php">Search</a> function.
[Edited on 7/26/13 by bfesser]
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Mailinmypocket
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I get all my bottles, vials etc from Qorpak. The green caps are PTFE lined and stand up to almost anything. They also have some Teflon lined septum vials, which also work nicely for
nasties (provided you don't puncture them, obviously). I got some from Dr.Bob a while back and liked them so much I bought more from Qorpak  Maybe check with him first as he might be able to give you a good deal on Teflon
lined bottles.
Some examples:
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Fantasma4500
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you can as if you have it laying around by now take something coneshaped and cover in aluminium foil, then shove it carefully yet with power down the
bottle opening, so that it will be completely sealed with aluminium
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CaliusOptimus
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Careful with that silver nitrate, it stains everything... and you won't know it until a week later!
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golfpro
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I have my nitric acid in a glass bottle with a glass stopper that doesn't quite fit, just a tad bit too big and infact if the acid is swirled, white
fumes come out a bit. This is stored in the garage. I plan on using it/getting rid of it within a week probably.
During the whole process, I avoided fumes for the most part (you immediately feel it on your sinus) and all work was done outside however I had one
kind of nasty inhalation of the fumes, I've heard of breathing the fumes can cause a serious medical emergency, but is this from prolonged exposure or
will a few whiffs cause a serious problem?
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golfpro
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So the nitric acid from H2SO4/KNO3 in the correct ratio (I forgot which) even from a retort will be almost pure aside from NO2 contamination? Is there
anyway to remove that?
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